As known, the attention to the conditions of health and hygiene in closed environments in which individuals operate is always higher, both for those buildings (hospitals, clinics, nursing homes, healthcare homes, and the like) where absolute lack of pollutants, pathogens, microbes, etc., is an essential obligation by the very nature of the activities that take place in these buildings, and, more in general, for any place, whether public or private, in which one or more people are likely to stay for longer or shorter periods.
Furthermore, it is appropriate to observe that in the air that is breathed inside closed environments, various types of pollutants and/or potentially dangerous to humans are contained. In addition to dust and particles of varying size (from a dimension of a few microns up to nanometers), it is in fact possible, for example, to find in the air toxic gases or micro-organisms of various nature (viruses, bacteria, spores, moulds, fungi, etc.). Furthermore, sometimes a lack of negative ions is detected, which de facto determines a sort of “electrical” pollution, which has to be counteracted to ensure the optimal conditions of hygiene and healthiness.
The precautions or the remedies that are normally adopted usually consist of selective action filters, directed, that is to say, towards a specific category of undesirable substance (and often, as in the case of anti-particulate filters, they prove to be ineffective against particles of finer dimensions).
Therefore, it appears evident how it is difficult, if not impossible, to ensure filtering, and the elimination of all the different types of polluting substances, as vice versa required by the increasingly stringent hygienic/sanitary requirements, unless resorting to complex infrastructures and plants of difficult installation which, due to high costs and/or to logistical problems, often prove uneconomic (and therefore unusable) for most of the applications.